Electricity Chapter 13.

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2 Charge and ForceAll matter is made of atoms that contain electrons, neutrons, and protonsRecall that protons and electrons in atoms have electric chargeElectrons have a negative chargeProtons have a positive chargeWhen an object has an equal number of protons and electrons, the object has no charge

3 Neutrons have no chargeNeutrons have no effect on the chargeCharges in objects can produce a force between the objectsObjects are forced together or attracted when their charges are different“Opposite charges attract”Same electric charges they push apart“Like charges repel”

4 Moving charges. Electrons can be moved aroundRubbing fur or cloth against rubber (like a balloon) will move some electrons from the cloth to the balloonBoth the cloth and the balloon will have a charge.What will the charge on the balloon be?What will the charge on the cloth be?

5 Electric Field Don’t have to touch to feel a charge.An electric field surrounds all charged objects.Electric forces act at a distance because or this field.

6 Static Electricity Static means not movingStatic electricity is electricity at restFriction can cause itObjects rub together and electrons move from one object another.

7 Two ways to move electronsConduction: electrons are transferred by direct contact.Induction: electrons on an object are rearranged without physical contact.

8 Two types of materialsConductors: a material through which electric charges move easily.Metals are good conductorsInsulators: a material through which electric charges can’t move easily.Plastics, rubber, ceramics, wood

9 ElectroscopeFlaskMetal bar (conductor) through rubber stopper (insulator)Two pieces of thin foil on the bottomCharge on the metal will push the foil apartbecause they have the same charge

24 Electric Current Electrons in motion.Current: The number of electrons that pass a specific point in a circuit in one secondVoltage: how hard the electrons are being pushed.Circuit: electric current flows through a closed, continuous path.

25 Generating Electric CurrentElectrochemical cell: (battery) changes chemical energy into electric energy. Two types wet cell and dry cell.Thermocouples: a tool that uses differences in temperature to generate electric currents.Generator- next chapter but make alternating current

26 Types of currentDirect current: electrons that flow in the same direction in a wire. (DC)From batteriesAlternating current: electrons that flow in different directions in a wire. (AC)From GenratorsUsed in your homeTransformers change AC to DC

27 Measuring ElectricityCurrent: The number of electrons that pass a specific point in a circuit in one secondMeasured in Amperes or amps (A)Voltage: how hard the electrons are being pushedMeasured in volts (V)Higher voltage, the more work the electrons can do.

29 Ohm’s LawThe relationship among current, voltage, and resistance.Ohm’s law states that the current in a circuit is equal to the voltage divided by the resistanceI = V RVIR

30 Do the MathA car has a 12 volt system. The headlights are on a 10 amp circuit. How much resistance do they have?Your house uses 120 volts. What amount of current would flow through a 20 ohm resistor?

31 Circuits For current to flow there must be a complete loopElectric circuit: complete, a closed path through which electrons travel.Electrons flow from negative to positive terminalWork is done if there is a resistance in the wire.

32 Circuits Resistance is supplied by a resistor.A resistor is a device that uses electric energy to do work.A wire connected from the resistor to the positive terminal completes the circuit.An open switch breaks the circuit.

33 Two Types of Circuits Series circuits: A circuit with only one path.All the resistors in a series circuit lie along a single path.The amount of current in a series circuit is the same at all parts of the circuit.Resistance in the circuit changes if resistors are added or taken away.

38 Parallel CircuitParallel circuits: The electrons in a parallel circuit can travel through more than one path, each path is separate.If there’s a break in one path in the circuit, electrons can still flow through the other paths and maintain a complete circuit.

41 Parallel circuits in your home allow each light or appliance to use the amount of current it needs to work.A parallel circuit prevents all the lights or appliances from shutting off when one of them stops working.

42 Electric power and energyPower: The rate at which electricity does work or provides energy The amount of electric power a device uses to do work is determined by its resistance.P = V x I(P) power = (V) voltage x (I) current in the circuit.

44 Electric safetyMany appliances are equipped with a “ground” wire on the plug.The ground wire prevents electric shock. The rounded third prong of a three-way electric plug is attached to the ground wire.It constantly moves static electricity from the appliance to the ground.

45 Broken wires or water can cause electric appliances to short-circuit.A short circuit occurs when electricity takes a short path and bypasses the resistors in the circuit.Because of this the resistance of the circuit is less and the circuit wire increases.The increased current can produce enough heat to melt wires and start a fire, or cause serious electric shock.

46 Circuit protectorsFuses and circuit breakers protect against overloaded circuits.A number on the fuse indicates the max. current that will flow through it.Circuit breakers are often used in place of fuses.A circuit breaker is a switch that opens automatically when electric current in a circuit reaches its max.